Lubricant composition for metal working operations

ABSTRACT

The lubricant composition comprises (a) a paraffinic base oil of defined viscosity and evaporation rate characteristics, (b) a polyhydric alcohol/aliphatic acid ester, and (c) an antiwear agent. The lubricant composition is especially suitable for use in punching and staged-drawing operations on a metal/alloy, e.g. steel.

This application is a 371 of PCT/GB98/02054, filed Jul. 13, 1998.

This invention relates to a lubricant composition for use in metalworking operations; more especially for use in metal-deformingprocesses, such as, for example, punching, pressing, forming and drawingprocesses. The invention is especially useful when the metal involved insuch a process is iron or an iron-containing alloy or is aluminium.

In such metal-deforming processes, especially severe operations onaluminium and steels, the lubricant employed must have the ability tolubricate fully throughout the process. An example of a severe operationis a three stage forming/drawing operation using mild steel to form acylinder 14.0 cm diameter, and 22.9 cm long. This process is normallylubricated with a lubricant at an operating temperature of 40 to 70° C.However, known lubricants result in substantial amounts of residuedepositing on the formed/drawn metal-product, which product then has tobe cleaned or degreased before it can pass to a further processing step,such as painting or dip-varnishing.

It is an object of the present invention to provide a lubricatingcomposition suitable for use in metal or metal alloy deformingprocesses, which composition has significantly decreased residue-formingcharacteristics while still retaining good lubricity characteristics.

According to one aspect of the present invention there is provided alubricant composition suitable for use in a metal or metal alloydeforming process, which composition comprises:

(i) a major proportion by weight of an essentially paraffinic base oilhaving a viscosity at 25° C. (ASTM D 445) of 2.00 to 2.75 mm²/s and anevaporation rate (DIN 53170) of from 400 to 700, (on a scale wherediethyl ether=1);

(ii) a minor proportion by weight of a polyhydric alcohol ester of analiphatic acid;

(iii) an amount by weight, which is less than that of (ii), of anantiwear agent; and

(iv) from 0 up to 10/% by weight of an antioxidant.

Preferably, the base oil component (i) is essentially iso-paraffinic.The preferred viscosity range for the base oil is preferably 2.00 to2.60 mm²/s, very preferably from 2.25 to 2.60 mm²/s. The viscositiesare, as previously stated, measured at 25° C. A base oil component (i)used in the invention of viscosity of 2.44 mm/s² at 25° C., will have aviscosity of 1.85 mm/s² at 40° C. A typical commercial spindle oil has aminimum viscosity at 40° C. of 10 mm²/s, whilst a typical commercialcylinder oil has a viscosity in the broad range 30 to 50 mm^(2/)s at 40°C.

The preferred said evaporation rate is from 450 to 700, more especially600 to 700. Normally, the base oil is present in an amount of at least75 wt. %; preferably at least, 80 wt. % or 90 wt. % or 95 wt. %,according to the process for which the composition is intended.

The said ester component (ii) is preferably an oleic acid ester. Thepolyhydric alcohol moiety is normally pentaerythritol. Pentaerythritoltetraoleate (PETO) is a preferred component (ii). The ester componentcan be present in an amount up to 15 wt. %, or up to 10 wt. %, moreusually up to 5 wt. %.

The antiwear agent, component (iii) may be, for example, zincdithiophosphate (ZnDTP) or other known agent. Preferably, it is an amineneutralised phosphoric acid ester of at least one aliphatic alcohol,especially an aliphatic amine neutralised such ester. Noramlly, up to2.5wt. % of component (iii) is employed (but less than component (ii)).The wt. % ratio of components (ii) and (iii) is, preferably, from 1.5:1to 10:1, suitably 2:1 to 8:1.

Optionally the lubricant according to the invention may include up to 1wt. % of an antioxidant, suitably up to 0.5 wt. %, or up to 0.2 wt. %.This component may be any suitable known antioxidant, preferably2,6-di-tert butyl 4-methyl phenol.

In accordance with another aspect, the invention provides a concentratesuitable for use in preparing a lubricating oil composition-definedabove; which concentrate comprises a solution or dispersion in a baseoil defined above, of (a) a polyhydric alcohol ester of an aliphaticacid, (b) a lesser amount of an antiwear agent, preferably being anamine neutralised phosphoric acid ester of at least one aliphaticalcohol and, optionally, (c) an antioxidant; (a) and (b) being presentin a weight ratio of from 1.5:1 to 10:1, preferably 2:1 to 8:1.

In accordance with a still further aspect, the invention provides ametal deforming process, more especially a steel deforming process,employing as the, or a, lubricant, a composition defined above orprepared from a concentrate defined above. The deforming process may be,for example, metal-punching a steel sheet. A preferred lubricantcomposition of the invention for use in such a process containsconstituents (ii) and (iii) in total amount of 1 to 2 wt. % and in ratio1.5:1 to 3:1. For use in another deforming process, viz. two-stagesteel-drawing process, a preferred lubricant contains constituents (ii)and (iii), in total amount of 10 to 20 wt. % and in ratio 2:1 to 8:1.

Some comparative tests were made between two commercially availablemetal working lubricant compositions (A and B), and a composition (C)which is one in accordance with the present invention. Compositions Aand C are mineral oil based and composition B is synthetic ester based.Components and characteristics of these compositions are given in TableI.

The three compositions were subjected to thermogravimetric analysis(TGA). The TGA was conducted under nitrogen in three steps (a) up to125° C. at 5° C. per min. (b) held at 125° C. for 20 min. and (c) from125 to 300° C. at 5° C per min. Residue % was measured.

The results of the tests are shown in Table II.

It will be seen from Table II that the TGA residue % from composition Cis very much lower than those from the known compositions. Thisillustrates substantial superiority for the composition of the inventionunder the practical conditions of severe metal-deformation processes.The resulting metal product will require no, or very significantly less,cleaning or degreasing before being ready for a further processing stepe.g. painting or varnishing. One contributing factor for saidsuperiority is illustrated in Table II by step (a) of the TGA test.There has been appreciably more evaporation of the oil in composition C(the invention) over the temperature range up to 125° C.

The invention includes, in a further aspect, the use of lubricantcompositions as herein defined in a metal working process, including themetal-deforming processes generally and particularly referred to herein.One such process is a two-stage metal-drawing process. That two-stageprocess is not possible with the foregoing compositions A and B. Thelatter provide insufficient lubrication throughout the full process,leading to case-splitting.

TABLE I The Compositions A B C Base Oil <1.70 <2.40 2.44 Viscosity @ 25°C. (mm²/s) Evaporation Rate 400 to 500 500 to 600 650 to 700 (diethylether = 1) Additives Ca phenate YES) NIL NIL ) 4.5% Zn DTP YES) NIL NIL) in PETO NIL) NIL YES) 1.5 wt. % ) total ) in Antiwear Agent ZnDTP) NIL(iii) herein) total

TABLE II The Results A B C TGA % step (a), up to 125° C., 94.6 88.4 98.2% evaporated TGA % residue 3.40 11.09 1.12

What is claimed is:
 1. A lubricant composition suitable for use in a metal or metal alloy deforming process, which composition comprises: (i) at least 75% by weight of an essentially paraffinic base oil having a viscosity at 25° C. as determined by ASTM D 445 of 2.00 to 2.75 mm²/s and an evaporation rate as determined by DIN 53170 of from 400 to 700, on a scale where diethyl ether=1; (ii) a major proportion by weight of a polyhydric alcohol ester of an aliphatic acid; (iii) an amount by weight, which is less than that of (ii), of an amine neutralized phosphoric acid ester of at least one aliphatic alcohol as antiwear agent, the weight ratio of (ii) to (iii) being from 1.5:1 to 10:1; and (iv) from 0 up to 1% by weight of an antioxidant.
 2. A composition as claimed in claim 1, wherein the base oil has a said viscosity of from 2.25 to 2.60 mm²/s.
 3. A composition as claimed in claim 2, wherein the base oil has a said evaporation rate of from 600 to
 700. 4. A composition as claimed in 3, wherein component (ii) is pentaerythritol tetraoleate.
 5. A composition as claimed in claim 4, wherein component (iv) is 2,6-di-tert butyl 4-methyl phenol.
 6. A composition as claimed in claim 4, wherein the base oil is present in an amount of at least 80 wt. %.
 7. A composition as claimed in 4, wherein component (ii) is present in an amount up to 15 wt. %.
 8. A composition as claimed in claim 7, wherein component (iii) is present in an amount up to 2.5 wt. %.
 9. A composition as claimed in claim 8, wherein the weight ratio of components (ii) and (iii) is from 2:1 to 8:1.
 10. A concentrate suitable for use in preparing a lubricating oil composition which concentrate comprises a solution or dispersion, in a paraffinic base oil, having a viscosity at 25° C. of 2.00 to 2.75 mm²/s as determined by ASTM D 445 and an evaporation rate of from 400 to 700 as determined by DIN 53170, on a scale when diethyl ether=1, of an amount of (a) a polyhydric alcohol ester of an aliphatic acid, (b) a lesser amount of an amine neutralised phosphoric acid ester of at least one aliphatic alcohol, (a) and (b) being present in a weight ratio of from 1.5:1 to 10:1.
 11. A metal deforming process employing as the lubricant, the composition of claim 1, 6 or
 9. 12. The concentrate of claim 10 wherein (a) and (b) are present in the weight ratio of 2:1 to 8:1.
 13. The concentrate of claim 10 wherein (a) is pentaerythritol tetraoleate, (b) is an aliphatic amine neutralized phosphoric acid ester of at least one aliphatic alcohol, the concentrate including an antioxidant.
 14. The concentrate of claim 13 wherein the antioxidant is 2,6-di-tert butyl 4-methyl phenol. 